A motor or a generator as a rotating electric machine mounted on a vehicle such as cars includes a rotor, and a stator in an annular shape arranged annularly around the rotor. With the motor, torque is obtained when a current passes through the stator, while with the generator, a current is obtained when the rotor rotates.
A stator includes an annular stator core having stator winding. The stator core has a plurality of annularly arranged divided cores, with an external cylindrical ring being fastened to an outer circumferential surface of the stator core.
When fixing the stator to a motor case, alignment and centering between the stator and the motor case is usually performed with an alignment mechanism using a pin or the like provided on the external cylindrical ring. When fastening the external cylindrical ring to the annularly arranged divided cores, however, the external cylindrical ring is heated and cooled by shrink fit and molding resin sealing, which may result in radial misalignment of the alignment mechanism using a pin or the like.
For example, even if the alignment mechanism using a pin or the like is provided between the external cylindrical ring and the motor case with reference to an inner diameter of the external cylindrical ring, the external cylindrical ring will be deformed due to heating and cooling if shrink fit is employed.
FIG. 20 is a perspective view of an external cylindrical ring 120. External cylindrical ring 120 has a cylindrical shape with open opposite ends, with a flange 122 extending radially outward being provided along the entire circumference of one of the ends. Flange 122 includes wide regions 123 each having a bolt hole 123h for use when fixing external cylindrical ring 120 to a motor case, and an alignment hole 123p into which an alignment pin fits if the alignment pin is provided on the motor case as an alignment mechanism. Alternatively, the alignment holes may be provided in the motor case and the alignment pins may be provided on the external cylindrical ring as an alignment mechanism.
FIG. 21 is a schematic cross-sectional view showing a state where divided cores 110 have been fixed using external cylindrical ring 120 by shrink fit. If external cylindrical ring 120 is not deformed, external cylindrical ring 120 is completed with an inner diameter (φD1) as was designed, and the alignment mechanism (not shown) using alignment holes 123p and the like provided on flange 122 of external cylindrical ring 120 is also completed with designed dimensions.
As shown in FIG. 22, however, when shrink fit is employed, external cylindrical ring 120 contracts when cooled, causing a high internal pressure (direction of an arrow F in the figure) to be applied from a stator core 111 to an inner surface of external cylindrical ring 120. External cylindrical ring 120 is thus deformed. The amount of deformation is greater on the side of external cylindrical ring 120 where flange 122 is not provided, due to its lower rigidity.
Accordingly, external cylindrical ring 120 is deformed, resulting in misalignment of alignment holes 123p provided in flange 122. It is noted that FIG. 22 exaggerates the actual amount of deformation to facilitate understanding of the deformation of external cylindrical ring 120.
An alignment mechanism may be provided after an external cylindrical ring is fastened to a stator core. This requires additional work and additional members, however, causing an increase in manufacturing cost of a rotating electric machine. A stator having a structure in which annularly arranged divided cores are fastened using an external cylindrical ring is disclosed in the following patent literature.